A 1-MHz-Bandwidth Gm-C-Based Quadrature Bandpass Sigma-Delta Modulator Achieving −153.7-dBFS/Hz NSD With Background Calibration

This paper presents a fifth-order continuous-time Gm-C-based quadrature bandpass sigma-delta (ΔΣ) modulator for Internet-of-Things applications. In the presented ΔΣ modulator, a reconfigurable full-scale input amplitude assists the ΔΣ modulator, achieving a wide dynamic range (DR) and a low-noise floor. A following system-level supply voltage and temperature background tracking technique stabilizes the frequency response of the Gm-C-based quadrature bandpass ΔΣ modulator. Furthermore, the 1.5-bit feedback current DAC employs a PN-based semi-self-swapping logic to relax the matching requirement. The prototype ΔΣ modulator was fabricated in a 180-nm CMOS process with an active area of 0.28 mm2. The ΔΣ modulator achieves a total DR of 93.7 dB with the reconfigurable full-scale input amplitude, resulting in a noise spectral density of -153.7 dBFS/Hz with a bandwidth of 1 MHz. The presented ΔΣ modulator consumes 2.0 mW with a power supply of 1.8 V and a sampling frequency of 32 MHz.